Gelation of hydrazine and hydrazine-type rocket fuels

ABSTRACT

This patent describes novel gelled hydrazine-type fuels suitable for use in rockets, missiles and the like. The gelling agents are quaternary ammonium slats of polyacrylic acid.

ilniied Siaies Pateni [1 1 Vander Wall et a1.

[ 1 Aug. 7, 11973 1 1 GELATlON 0F HYDRAZINE AND HYDRAZlNE-TYPE ROCKETFUELS [75] Inventors: Eugene M. Vander Wall, Citrus Heights; James M.Lucas, El Dorado Hills, both of Calif.

[73] Assignee: Aerojet-General Corporation, El

Monte, Calif.

[22] Filed: July 27, 1967 [21] Appl. No; 658,982

[52] US. Cl. 149/36, 49/20 3,164,505 1/1965 Hsieh et a1 149/36 3,196,0597/1965 Godfrey 149/36 X 3,197,348 7/1965 Skolnik et al.... 149/36 X3,232,801 2/1966 Bost et a1 149/36 X Primary ExaminerCar1 D. QuarforthAssistant Examiner-Stephen .I. Lechert, Jr. Attorney-Edward O. Ansell,D. Gordon Angus and Donald W. G rauer [57] ABSTRACT This patentdescribesnovel gelled hydrazine-type fuels suitable for use in rockets, missilesand the like. The gelling agents are quaternary ammonium slats ofpolyacrylic acid.

7 Claims, N0 Drawings GELATION OF HYDRAZINE AND HYDRAZINE-TYPE ROCKETFUELS BACKGROUND OF THE INVENTION The field of the present inventionpertains to gelled rocket fuels.

Various hydrazine-type fuels are well known for use in liquid rocketengines. However, liquid hydrazinetype materials are characterized byseveral problems. One of these is the tendency to slosh within fueltanks during flight. Sloshing has been found to adversely affect thestability of the rocket. Liquid hydrazene fuels also present a safetyhazard since they can easily escape through ruptured or perforated tanksor fuel lines. For these and other reasons, various gelling agents havebeen proposed to thicken or produce a mechanically stable gel ofhydrazine. One example of such a gelling agent is polyacrylic acid whichis disclosed in assignees U.S. Pat. No. 3,232,801 issued Feb. 1, 1966.This patent describes the use of polyacrylic acid as a gelling agent toproduce a mechanically stable, thixotropic hydrazine-type gel. Thecompositions of this patent are quite satisfactory in most respects.However, certain significant improvements have now been discovered andthe present patent application is directed to these improvements.

SUMMARY OF THE INVENTION Briefly, the present invention comprises agelled, mechanically stable, thixotropic liquid fuel compositioncomprising a hydrazine-type fuel containing an effective gelling amountof a gelling agent which is a quaternary ammonium salt of polyacrylicacid. The invention further comprises a method of preparing novel gelledfuel compositions.

As has been indicated above, it is desirable to gel rocket fuels so thatthe liquid is immobilized to reduce seepage and leakage hazards, andprevent sloshing of the liquid in propellant tanks. It is also desirableto gel rocket fuels so that solid energetic particles, usually solidmetals, can be permanently and uniformly suspended in the fuels toincrease the fuel value. Gelation also aids in holding the propellant inits position in fuel tanks under conditions of gravity. The quaternaryammonium salts of the present invention are superior to known gellingagents in that at concentration levels of less than percent, they willgel fuels that cannot be gelled by the incorporation of ordinarypolyacrylic acid. The quaternary ammonium salts of the present inventioncan also be used to gel several different types of hydrazine-type fuelsand are not restricted in their use to the gellation of ordinaryhydrazine or hydrazinecontaining mixtures.

The gels of the present invention are also less sensitive to ioniccontamination than are other polymers used for gelation. The hydrazinegels of the present invention have been found to be stable over agreater temperature range than hydrazine gelled with polyacrylic acid.Further, the gelling agents of the present invention can be completelyneutralized so that no acidic species are introduced into the fuels,making the fuels less reactive with acid-sensitive metals and compounds.

Accordingly, it is a principal object of the present invention toprovide a mechanically stable, thixotropic gelled hydrazine-type fuelcomposition.

Another object of the present invention is to provide a means of gellinghydrazine-type fuel compositions having a wider applicability than haspreviously been available.

Still another object of the present invention is to provide a gelledhydrazine fuel composition which is stable over a greater temperaturerange than known gelled hydrazines.

It is still another object of the present invention to provide a gelledhydrazine-type fuel which is less sensitive to ionic contamination.

A further object of the present invention is the provision of a gelledfuel composition which is less reactive with acid-sensitive metals andother fuel additives.

These and other objects and advantages of the present invention willbecome apparent from a more detailed description which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The gelling agents of thepresent invention are normally employed in effective gelling amounts upto about 10 percent by weight of the total fuel composition. However, itshould be understood that even greater amounts of the gelling agent maybe employed, although this is normally to be avoided since the gellingagents are completely effective at low concentration and the use of moregelling agent is of no further benefit.

There may be included in the gelled hydrazine-type fuels of the presentinvention, as an optional ingredient, powdered metals such as aluminumor beryllium. These metals serve to increase the specific impulse of thefuel. The amount of powdered metal employed is not critical. Normally,if the powdered metal is added, it should be used in amounts up to aboutpercent by weight of the total weight of the gelled fuel compositions.When these metals are incorporated in the gelled hydrazine compositions,it has been found that the resulting fuel is mechanically stable andthere is no tendency for the powdered metal to settle out of the gel.

The quaternary ammonium polyacrylate salts used as the gelling agents ofthe present invention are prepared by neutralizing a suitablepolyacrylic acid with a quaternary ammonium hydroxide in a solvent. Thesolvent is removed after neutralization and the salt is dried in vacuumat room temperature.

The amount of quaternary ammonium hydroxide used may be enough toneutralize all of the free carboxyl groups in the polyacrylic acid.However, in many cases, less than a stoichiometric amount of quaternaryammonium hydroxide is used. The use of partially neutralized polyacrylicacid has been found to reduce the quantity of a gelling agent which isrequired for gellation compared to that required when the completelyneutralized salt is used. In other cases where acid sensitive metals orother additives are to be employed, it has been found that it ispreferred to employ a completely neutralized gelling agent whichintroduced no acidic species into the fuels. Thus, based upon theforegoing criteria, those skilled in the art will be able, within thescope of the present invention and in accordance with the teachings ofthis patent, to select a gelling agent to provide optimum gelation ineach specific fuel composition while minimizing the amount of gellingagent required.

The following examples are presented solely to illustrate the inventionand should not be regarded as limiting in any way. In the examples, theparts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 The following example illustrates the preparation of thegelling agent of the present invention. 5.42 grams (0.72 equivalents) ofsuitable polyacrylic acid, Cartetrapropyl ammonium hydroxide in theabove example, tetramethyl ammonium polyacrylate and tetraethyl ammoniumpolyacrylate were obtained.

TABLE I Components of gels Physical properties High shear Gallantviscosity Gel is cone. (01).) (17,300 stable lolyacrylate gelling agent(percent) Fuel sec. to-( F.)

Tr-tramr-thyl-ammoniurn 1.37 Hydrazine 37 165 Tetraethyl-ammonium 1. 83.d 165 Tetrapropyl-ammoniu 1.40 26 165 Tetraethyl-ammonium. 8. 1 3-1'Ietrapropyl-ammonium. 4.1 24 165 Tetrapropyl-ammonium 34 neutr 2.0 ..do23 133 Tetrapropyl-ammonium 3.7 33 212 D0 6 {50% unsymmetrical (limethylhydrazine. "II;

bopol-940, a polyacrylic acid manufactured by B. F. The hydrazine gelsprepared with quaternary ammo- Goodrich Company, are dispersed in 550 mlof methanium salts do not break down upon prolonged exposure nol. Asthis solution is stirred, 142 grams of a 10 perto the atmosphere, whilehydrazine gels prepared with 35 cent aqueous solution of tetrapropylammonium hydroxide (0.072 equivalents) available from Eastman ChemicalProducts Company are gradually added. The entire addition requires fiveminutes. A gel forms, and stirring is continued for two hours to assurecomplete mixing. Methanol and water are removed by evaporation undervacuum. The product is vacuum-dried at a pressure of 5 mm Hg for fourdays at room temperature. The product is a glass-like material whichrequires grinding to facilitate dispersal in liquids. The yield is 19grams of tetrapropyl ammonium polyacrylate which corresponds to 97percent of the theoretical yield. Losses are primarily incurred inhandling. The pH of an 0.01 N solution of tetrapropyl ammoniumpolyacrylate in water is 8.8. The equivalent weight of this salt is 260.

By substituting tetramethyl ammonium hydroxide and tetraethyl ammoniumhydroxide, respectively, for

the polyacrylic acid itself break down upon brief exposure.

The following tables illustrate the properties various gels within thescope of this invention.

High Yield Gel Gelling shear stress, breakdown agent, vlseosdynes/tempera- Gelling agent percent ity, cp. cm! ture, F.

Tetramethyl ammonium polyacry ate 0. 94 25 600 165 D0 1. 47 64 2, 800165 Tetrapropyl ammonium polyacrylate 1. 40 26 165 Do 1. 88 46 600 165Tetrabutyl ammomum aerylate 2. 92 14 300 Property not determined.

TABLE 1II.-PROPERTIES OF METALIZED HYDRAZINE GELS Yield High Gel-liquidComposition stress, shear transition dynes/ viscostempera- Gellingagent- Pereent Metal em. ity, cp. ture. F.

Tetramethyl ammonium polyacrylate 0.58 43% A1 1,800 50 D0 0.48 43% Al 30160 Tetramethyl ammonium polyacrylate 50% neutralized 0. 48 43% -18 160'Ietrapropyl ammonium polyacrylate 1. 2T 43% Al 1, 200 52 160 Do 0.5843% Al 28 160 Do 0.91 LM-Q 1,000 39 160 Property not determined.

lNG AGENTS Gelling agent High Yield G el conccnshear stress, stabilitytratiou, viscosdynes/ temperature (iclling agent Fuel percent ity, op.cm.'- limits, F.

Totravthyl ammonium polyacrylate Monomethyl hydrazine 8. 1 34 t) (l'letrapropyl ammonium polyacrylatm 4. O 20 100 65, 16a Do 8.6 67 2,20065, 165 'lotrabutyl ammonium polyaciylatc "do 12.9 16 t) 65, 165

Property not determined.

in general, it can be seen from the foregoing examples that the stablehydrazine gels of this invention are produced by mixing a gelling agentwith hydrazine. it is to be understood that powdered metals such aspowdered aluminum, can be blended either before, after, or along withthe gelling agent. The ingredients are normally blended by shaking or bymechanical agitation to uniformly distribute the gelling agent and todeagglomerate the powdered metal.

The significant improvement in the gel stability in the presence of ionsis shown by the comparative data on the following table.

TRA'IION ON THE HIGH SHEAR VISCOSITY OF HYDRA- ZINE GELLED WITH SALTS OFPOLYACRYLIC ACIDS Monomethylhydrazonium salt of TF/I RAP ROI YLAMMONIUMSAL'I OF POLYAC RYLIC ACID Gallant Sodium concentration nitrateViscosity /O) (m -l (an) 1. 40 0 26.011. 2 1.33 51 23. 110. 8 1. 33 9819. :121. 2 1. 33 337 16. Git). 2

Nora-All viscosity measurements are reported at a shear rate of 17,300secf While the present invention has been specifically illustrated withhydrazine monomethyl hydrazine and unsymmetrical dimethyl hydrazine, itis to be understood that it is applicable to all types of hydrazine-typefuels, including mixtures of various hydrazine-type fuels.

The gelled fuels of the present invention are highly energetic and aredirectly useful as fuels in liquid rocket motors.

As can be seen from the foregoing discussion, the gelled fuels of thepresent invention can be made quite insensitive to acidic reactingliquid propellant additives. The gels of this invention are also stableover a wide range of temperatures. In addition, the gelling agentsemployed in the present invention can be varied in accordance with theparticular fuel to be gelled. Thus, if the fuel is to contain anacid-reacting ingredient, the gelling agent can be completelyneutralized. On the other hand, if no acid-reacting additive is to beemployed, then, the gelling agent. need only be partly neutralized, andin this case the amount of gelling agent required can be reduced. it istherefore apparent that the present invention will find wide applicationin the space and defense missile efforts.

Having fully described the invention, it is intended that it be limitedonly by the lawful scope of the appended claims.

We claim:

1. A gelled mechanically stable thixotropic highenergy fuel compositioncomprising a hydrazine-type fuel selected from the group consisting ofhydrazine and alkyl substituted hydrazines containing therein aneffective gelling amount of a gelling agent comprising a quaternaryammonium salt of polyacrylic acid.

2. The composition of claim 1 wherein the gelling agent is tetramethylammonium polyacrylate.

3. The composition of claim 11 wherein the gelling agent is tetraethylammonium polyacrylate.

4. The composition of claim 11 wherein the gelling agent is tetrapropylammonium polyacrylate.

5. The composition of claim 11 wherein the gelling agent is tetrabutylammonium pol yacrylate.

6. The composition of claim 1 wherein the gelling agent comprises apartially neutralized quaternary ammonium salt of polyacrylic acid.

7. The composition of claim 1 wherein there is additionally presentfinely divided metal fuel in an amount up to about 60 percent by weightof. the composition.

, a a t a a

2. The composition of claim 1 wherein the gelling agent is tetramethyl ammonium Polyacrylate.
 3. The composition of claim 1 wherein the gelling agent is tetraethyl ammonium polyacrylate.
 4. The composition of claim 1 wherein the gelling agent is tetrapropyl ammonium polyacrylate.
 5. The composition of claim 1 wherein the gelling agent is tetrabutyl ammonium polyacrylate.
 6. The composition of claim 1 wherein the gelling agent comprises a partially neutralized quaternary ammonium salt of polyacrylic acid.
 7. The composition of claim 1 wherein there is additionally present finely divided metal fuel in an amount up to about 60 percent by weight of the composition. 